The performance of civil and military operations, such as responses to emergencies and operations in remote or non-friendly territory, can be seriously compromised if communication links are poor. Unfortunately, communication links often are poor in such territories, either as a result of natural or military disruption of pre-existing permanent links, or as a result of there being no or few such permanent links in the first place.
A great deal of research has been done in recent years into the performance of opportunistic telecommunications networks, which do not rely on the existence of pre-existing fixed links. Many such networks, for example networks established on an ad hoc basis between mobile phones or between road vehicles, require a high density of devices able to participate in the network; clearly, that will often not be available in post-disaster, conflict or similar areas. Furthermore, many operations have requirements beyond mere connectivity—for example, security requirements may necessitate restricting data to trusted network devices, and in many cases to trusted network devices specifically rated to handle the sensitive information—which can reduce still further the number of available nodes in a network.
Most work in this area has concentrated on devising and investigating different forms of routing. Some work has also been done considering the best choice of bearer for links. One approach adopted in the area of tactical (military) communications is provision of dedicated communications unmanned aerial vehicles (UAVs). However, UAVs are very expensive. Another approach is to mount network communications devices on vehicles that have a primary function that is not communications, for example, transport aircraft. By extending the range of possible platforms that can be employed, the number of available platforms can be increased significantly; however, typically the non-dedicated vehicles will be available only intermittently, according to the requirements of their primary function. Networks incorporating such “non-communication assets” are referred to as “opportunistic networks”, often taken to be a sub-class of Disruption/Delay Tolerant Networks. Such networks have been studied with a view to optimising the routing of communications data over their links, in view of their intermittent nature.
In “Routing Strategies in Multihop Cooperative Networks”, IEEE Transactions on Wireless Communications, Vol. 8, No. 2, February 2009, Gui et al present a study of outage performance, taking into account the fading characteristics and broadcast nature of wireless channels, for three different routing strategies: optimal routing, in which the source-to-destination path with the largest minimum signal-to-noise ratio (SNR) is chosen; ad-hoc routing, in which the hop with the highest SNR is chosen at each node from available next hops; and N-hop routing, in which the path with the largest minimum SNR over groups of N hops is chosen. Optimal routing is found to give the best outage performance, but at the expense of greatly increasing complexity of calculation for routing over more and more hops. Ad-hoc routing suffers from greater outage, but the complexity of calculation is the same regardless of the number of hops. N-hop routing is a compromise that can provide a good trade-off between outage performance and complexity of calculation.
Despite these various efforts, there remain environments in which there are unlikely to be sufficient dedicated communications nodes in a deployable network to provide communication links of the desired quality. Of the approaches discussed above, the use of communication nodes on non-communications assets to work on an opportunistic basis is a more cost-effective approach than using dedicated communications UAVs, but such non-communications assets provide only “nodes of opportunity”, which will usually be far from optimal. Prior-art attention has generally been focused on mobile ad hoc network (MANET) issues.
The present invention seeks to mitigate the above-mentioned problems.